1. Field of the Invention
The present invention relates to methods for formulating compound fertilizers, including prescribing optimum ratios, quanta, and concentrations of constituent nutrients of compound fertilizers.
2. Scope and Usage of Certain Terms
The following lexicon sets forth the intended scope and meaning of certain terms and concepts used in the present specification and claims. The definitions set forth below include singular, plural, and grammatical variations of the terms defined.
Compound fertilizer−a mixture, formulation, or blend of two or more constituent nutrients, with or without non-nutrient supplements.
Stock—a supply of compound fertilizer, whether in solid (blend) or liquid (solution) form, formulated and held for future use.
Prescribe—to set forth or determine the type and the concentration and/or quantum of one or more constituents, including constituent nutrients, of a compound fertilizer.
Determine—unless explicitly narrowed, any process or activity employed to ascertain information such as, without limitation, actual values, theoretical values, quanta, ratios, and conditions.
Primary nutrient—a member of the class of essential plant nutrients comprising nitrogen (N), phosphorous (P), and potassium (K), frequently referred to collectively as “macro-nutrients” because they are required by plants in relatively large amounts.
Secondary nutrient—a member of the class of essential plant nutrients comprising calcium (Ca), magnesium (Mg), and sulfur (S).
Tertiary nutrient—a member of the class of essential plant nutrients comprising all essential plant nutrients not classified as primary or secondary. While there is no universal agreement as to the precise membership of this class, there is a general consensus that the following nutrients are tertiary nutrients: iron (Fe), manganese (Mn), copper (Cu), zinc (Zn), molybdenum (Mo), chlorine (Cl), and boron (B). Because of the relatively small amounts of these nutrients required by plants, they are frequently referred to as “micro-nutrients.”
Concentration—unless limited explicitly or by context, “concentration” is used broadly to include, for example, percent by weight, mass per volume, volume per volume, and parts per million (ppm). Concentration values are denoted herein by inclusion within square brackets ([ ]).
Irrigation water—is used in a broad context to include water, regardless of the source, that is applied to plants as an addition to or as an alternative to natural rain water.
Supplemented—refers to the addition of nutrients and/or other fertilizer constituents to irrigation water. Irrigation water to which nutrients and/or other fertilizer constituents have been added is referred to herein as “supplemented irrigation water.”
Ambient—refers to the composition or contents of irrigation water prior to supplementation. “Ambient” used to modify a nutrient refers to the naturally occurring quantum or concentration of the nutrient in the irrigation water prior to supplementation or alteration. An ambient concentration is denoted herein by square brackets and a subscript “a” ([ ]a). “Ambient pH” refers to the pH of the irrigation water prior to supplementation or alteration.
Exogenous—refers to a nutrient and/or the quantum or concentration of a nutrient used to supplement irrigation water.
Index nutrient, non-index nutrient—“index nutrient” (Nui) refers to a constituent nutrient of a compound fertilizer to which the quantum or concentration of at least one other nutrient in the compound fertilizer is pegged. “Non-index nutrient” refers to any constituent nutrient of a compound fertilizer other than the index nutrient.
Final concentration and final pH—respectively, the concentration of a substance in, or the pH of, irrigation water after the irrigation water has been supplemented according to the methods disclosed herein. A final concentration is denoted herein by square brackets and a subscript “f” ([Nui]f). The “target” or “desired” final concentration or pH is the final concentration of the nutrient or the final pH that is to be achieved by the methods disclosed herein.
Index ratio, Ri—the ratio between the final concentrations of an index nutrient and a non-index nutrient of a compound fertilizer.
3. Statement of the Problem Solved by the Invention
The problem solved by the present invention is how to prescribe the constituent nutrients of a compound fertilizer—particularly those formulated as “off-the-shelf” products”—in a way that takes into account variations in the ambient concentration of at least one of the constituent nutrients. This problem is of primary concern to those in the arts of agriculture and horticulture because plants must have access to each essential nutrient in at least a minimal amount in order to survive, yet most essential nutrients also have a toxic level above which the plant will die. Thus, for each essential nutrient there is a concentration range that must be adhered to, referred to herein as the “nutritional range.” If the level of only one essential nutrient falls outside this nutritional range, the plant will not thrive. The nutritional ranges of the primary nutrients are relatively wide, but with respect to the tertiary nutrients the difference between insufficient amounts and toxic amounts is quite narrow. Furthermore, the nutritional range and optimal concentration of a given nutrient may vary as a function of the plant's life cycle, ambient light, pH of the environment, and other variables.
Compounding this difficulty of determining the proper amounts or concentrations of multiple nutrients in compound fertilizers is the fact that nutrients when blended together can interact with each other, with counter ions, or with the solvent, normally water, in untoward ways. For instance, nutritionally beneficial concentrations of Ca or Mg in a compound fertilizer tend to precipitate from solution. This is an even more significant problem in areas having “hard” irrigation water; i.e., water with high ambient concentrations of Ca or Mg. The resulting precipitates can remove free nutrient from use by the plant and clog irrigation and spraying equipment. Nonchelated tertiary nutrients, if employed with many common phosphorus compounds, also tend to precipitate from solution. Consequently, in order to attain and maintain desired predetermined ratios of essential nutrients, one must be cognizant of and avoid counterproductive physiochemical conditions and interactions that alter the amount of free nutrients available for uptake by the plant.
4. Existing Art
The problem of ensuring that multiple nutrients are applied within their nutritional ranges has been traditionally addressed by ascertaining optimal ratios between the various components of the compound fertilizer. For instance, N—P—K fertilizers are commonly available in a variety of predetermined N:P:K ratios to accommodate diverse plant nutritional needs and environmental conditions. The literature contains many examples of the way nutrient ratios are determined and manipulated to carefully control the application rates of the nutrients. Commonly, nutrients in compound fertilizers are present in fixed ratios to exogenous nitrogen, without reference to ambient concentrations of N or Ca, or any other nutrient. U.S. Pat. No. 5,768,128 to Thompson et al. discloses a complex method of producing nutrient requirement maps for agricultural fields and using that information to formulate and apply appropriate fertilizer blends differentially to various areas of the field. Peters et al. (U.S. Pat. No. 5,114,459) disclose adjusting the ratio of ammoniacal nitrogen to nitrate nitrogen in compound fertilizer as a function of the amount of ambient light to which the plant is exposed. Greensides (U.S. Pat. No. 6,549,851) discloses a computer-based method of determining optimal amounts and ratios of plant nutrients based upon repeated plant tissue analysis during the growing season.
Avoiding untoward interactions between nutrients in a compound fertilizer is also a topic that is well addressed in the literature. The inclusion of chelating agents such as EDTA (ethylenediaminetetraacetic acid) to compound fertilizers is one common means for reducing precipitation of secondary and tertiary nutrients. For example, Vetanovetz et al. (U.S. Pat. No. 5,171,349) advocate using urea phosphate as the phosphate source in order to minimize precipitation of nonchelated secondary and tertiary nutrients, while Daniels (U.S. Pat. No. 6,858,058) discloses the inclusion of excess chelating or sequestering agents in the compound fertilizer.
Two major shortcomings of the foregoing methods and all other known methods of formulating compound fertilizers are: 1) they ignore the primary role played by Ca and the Ca:N ratio in plant nutrition, and 2) they fail to take into account ambient concentrations of nutrients, particularly ambient concentrations of Ca. While it is not uncommon to custom blend compound fertilizers based on ambient concentrations of one or more nutrients in the irrigation water, presently there is no method or system for conveniently prescribing ready-made fertilizer formulations that will provide reasonably precise and predetermined nutrient ratios over a wide variation of ambient nutrient concentrations, particularly ambient Ca. What is needed is a convenient and economical method of prescribing amounts or concentrations of nutrients in a compound fertilizer based on predetermined nutrient ratios and the ambient concentration of at least one index nutrient.